Cracking of hydrocarbons

ABSTRACT

A HYDROCARBON FEEDSTOCK, FOR EXAMPLE, NAPHTHA, IS CRACKED IN THE PRESENCE OF STEAM WHICH HAS BEEN PRODUCED IN THE PRESENCE OF AN ALKANOLAMINE, PREFERABLY ETHANOLAMINE. THE PROCESS REDUCES CORROSION IN THE STEAM-RAISING EQUIPMENT.   D R A W I N G

G. H. MANsFu-:LD ET AL 3,720,600

CRACKING OF HYDROCARBONS v Filed Mai-ovh 1, 1971 MM B /mm Attorney",

United States Patent O U.S. Cl. 208-47 11 Claims ABSTRACT F THE DISCLOSURE A hydrocarbon feedstock, for example, naphtha, is cracked in the presence of steam which has been produced in the presence of an alkanolamine, preferably ethanolamine. The process reduces corrosion in the steam-raising equipment.

We have now found that the problems of corrosion fby recycle water may be reduced if certain amine compounds are present in the water stream used to raise steam.

Accordingly the present invention is a process for cracking a hydrocarbon feedstock which comprises cracking the feedstock in the presence of steam which has been produced in the presence of an alkanolamine.

`Monoand poly-alkanolamines may be used in the process `but it is preferred to use monoalkanolamines, more preferably monoethanolamine.

The amount of alkanolamine used should preferably be sufficient to maintain the pH of the water used in the steam boilers above a value of 7, more preferably in the range 8 to 9. The alkanolamine per se may be added to the water or it may be added as a solution in a suitable solvent, for example ethanolamine in water. Alternatively, the alkanolamine or its solution in a suitable solvent may be added directly to the boiler.

The hydrocarbon feedstock is preferably a naphtha stream used in the preparation of oleiines.

One embodiment of the invention by Way of example will now be described with reference to the drawing which is a simplified flow diagram of a process according to the invention.

Naphtha feedstock at a temperature in the range 750 C. to 900 C. and a pressure inthe range 10 to 100 p.s.i.g. and steam at a temperature of 300 C. `are fed into a series of crackers 1 by lines 2 and 3 respectively. The cracked product comprising principally hydrocarbons, steam and hydrogen is passed to a primary fractionator 4 in which a heavy oil is separated as bottoms product and removed by line 5. The process hydrocarbons and water are removed overhead by line 6 and are passed to a secondary fractionator 7. Here the process gases are removed overhead by line 8 and the water, which may still contain some hydrocarbons, removed by line 9 to another fractionator 10. The remaining hydrocarbons are removed overhead by line 11 from fractionator 10 and recycled to fractionator 7. The water is removed from fractionator by line 12 into which is passed an ethanolamine stream 13. The mixed stream of water and ethanolamine then passes through a pump 14 to the dilution steam drums 15 from which steam is removed by line 3 and passed to the crackers.

The following table illustrates operations over a number of days and records details of the ethanolamine concentration in the Water stream, the iron content of water passing through pump 14 and the iron content and pH of steam leaving the boilers 1S. The iron content, of course, illustrates the extent to which corrosion is taking place.

3,720,600 Patented Mar. 13, 1973 ICC Boiler 15 Ethanol Pump 14, Fe Fe content, Day amine, p.p.m. content, p.p.m. pH p.p.m.

2 404.0 o. 1 s. 4 o. 4 40-50 0. 04 8. 4 0. 4 40-50 0. 06 8. 4 0. 4

0.08 8.4 0. 72 4 o. os s. 3 0. so 40-50 o. o4 s. 2 o. 3o

0. 0B 8. 7 0.6 5 o. 04 s. 5 0. 72 'ao-4o o. 06 s. o o. 6

0. 04 8. 2 0. 5 m so'g 5. 7 it 5 40 50 8. 0 1. 2

11 404,0 0. 05 8. 3 0. 4 Lurso o. o5 s. 2 o. 4 (l) 5. 3 1. 2

0. 05 8. 6 0. 8 12 agg ..1 o.. 40-50 8. 0 0. 4

0 0 04 8.5 1.3 14 Egggo 8. 6 1. 0 40-50 8. 7 0. 4

8. 5 0. 8 17 s. 7 o. 4s

1 Breakdown.

The figures in the table show that before ethanolamme was injected and at any time when a failure of the ethanolamine feed occurred, the iron content and acidity of the water leaving the boilers 15 Iboth rose. As soon as the ethanolamine feed was restored, the iron content and acidity both feel to very low levels.

We claim:

1. In a process for cracking a hydrocarbon feedstock in the presence of steam which involves separating water from the products obtained by cracking, converting the water thus separated into steam and using said steam in said cracking, the improvement whereby corrosion of equipment by said water is obviated, said improvement comprising incorporating an alkanolamine into the water before it is converted into steam for use in said cracking.

2. A process as claimed in claim 1 wherein the alkanolamine is a rnonoalkanolamine.

3. A process as claimed in claim 1 wherein the alkanolamine is ethanolamine.

4. A process as claimed in claim 1 wherein the amount of alkanolamine used is sufficient to maintain the pH of the water used for steam above :a value of 7.

5. A process as claimed in claim 4 wherein the amount of alkanolamine used is sufficient to maintain the pH of the water used for steam above a value in the range 8 to 9.

6. A process as claimed in claim 1 wherein the alkanolamine is added to the process in solution.

7. A process as claimed in claim 3 wherein the ethanolamine is added to the process in solution in water.

8. A process as claimed in claim 1 wherein the hydro- References Cited 125:21; ggltsck is a naphtha stream used 1n the prepara- UNITED STATES PATENTS 9. A process as claimed in claim 1 wherein: 3,562,146 2/1971 Deanesly 20S-'130 (a) a naphtha feedstock is cracked to form olenes 5 2,938,851 5/1960 Sedman. et al- 208-47 (b) water is condensed from the products of the 3,382,186 5/1968 Sllvefstem 252-390 cracking proeess KlYlen (c) the condensed water is converted to steam in the 3,629,353 12/1971 Reltsema et al- 260*683 presence of ethanolamine 2,908,640 10/1959 Dougherty 20s- 351 3,078,223 2/ 1963 Thompson 208-348 (d) the steam so produced is recycled for use in the 10 cracking process.

10. The process of claim 1 wherein the hydrocarbon DELBERT E GANTZ Pnmary Exammer feedstock is a naphtha feedstock and the alkanolamine G. E. SCHMITKONS, Assistant Examiner is ethanolarnine added in an amount suicient to maintain the pH of the water to above a value of 7. 15 U.S. Cl. X.R.

1l. The process of claim 10 wherein the naphtha feedstock is cracked at 750-900 C. and a pressure of 21 2.7 208 106 130 26o-683 R 10-100 p.s.i.g. using steam at a temperature of 300 C. 

